Gas Can Storage
The two answers people come here for: store gas cans SEALED (not vented), and the swelling you see on hot days is normal — manage temperature, not the vent. Gasoline vapor is heavier than air, drifts, pools, and finds ignition sources; every storage rule below follows from that one fact. Here is the full picture, from garage shelf to overland rack.
Sealed, not vented
A vented can releases flammable vapor into whatever space it sits in, continuously — the opposite of safe storage. Modern containers are engineered to hold vapor pressure; keep caps and spouts closed and gaskets in good shape. The right environment does the rest: shade or a cool outbuilding, off living spaces, away from water heaters, pilot lights, outlets, and anything that sparks. Fill to the marked capacity only — that last five percent of headspace is the expansion room the can needs.
Why cans swell, and when to worry
Vapor pressure rises with temperature, so a can in a 100°F shed bulges by design and relaxes at night. Worry when a can stays hard-swollen in cool shade, shows seam or weld stress, or weeps at the gasket — that is a container at the end of its life, and fuel is too cheap to trust a two-dollar failure point with a vehicle or a garage. Metal NATO-style cans handle pressure cycling and abuse better than thin consumer plastic; either way, sun is the enemy.
The trunk question
Transporting a full can home: acceptable — sealed, upright, secured so it cannot tip, windows cracked, straight home. Storing fuel in a trunk or inside a van: no. A closed vehicle is a heat box that concentrates vapor with you and your ignition sources sealed in alongside it. This matters double in a camper van — the vehicle is your bedroom. Fuel does not live inside the living envelope, period.
How overland rigs carry fuel right
The expedition answer is external carry: purpose-built mounts on a rear rack, bumper, or ladder, holding fuel-rated cans locked and vibration-secured, outside the cabin air space. It survives heat, spills, and accidents the way interior storage never can. Mounts, racks, and carriers sized and torqued to the vehicle are standard exterior mods work — and if the fuel plan is part of a bigger self-sufficiency build (water, power, recovery gear), that is the overland rig conversation, platform-planned from the start in a custom overland upfit. Weight placement questions (racks carry fuel high) tie into roof rack limits too.
Frequently asked questions
Should gas cans be vented when stored?
No — store them sealed. Modern cans are designed to contain vapor; an opened vent releases flammable fumes into the storage space continuously. The pressure swelling you see on hot days is normal and the can is built for it. Manage temperature (shade, stable cool storage) instead of cracking the vent.
How do you keep a gas can from expanding?
You mostly don’t — expansion and contraction with temperature is normal behavior, not a defect. Reduce it by storing out of direct sun, filling only to the can’s marked capacity (about 95%, leaving vapor space), and avoiding temperature swings. A can that stays grossly swollen in cool shade or shows seam stress should be replaced.
Can you keep a gas can in your trunk?
For transport home from the station, yes — filled to spec, sealed, upright, and secured, with windows cracked. As standing storage, no: a trunk is a sealed oven where vapor accumulates, and any spark event becomes catastrophic. Long-term fuel lives outside the passenger/cargo envelope — externally mounted or in a dedicated shed, never in a van you sleep in.
What is the right way to carry extra fuel on a van or overland rig?
Externally: purpose-built can mounts on a rear rack, bumper, or ladder — metal NATO-style cans or rotomolded containers rated for fuel, locked and secured against vibration. External carry keeps vapor out of the living space, survives a rollover better, and is how expedition vehicles have done it for decades.